1. Field of the Invention
The present invention relates to an electronic apparatus including a touch panel.
2. Description of the Related Art
An electronic apparatus such as a smartphone and a tablet, in which a touch panel is mounted, has come into wide use. The electronic apparatus may include an electrostatic capacitive touch panel. The electrostatic capacitive touch panel can receive “touch operation” performed by directly bringing a finger of a bare hand into contact with a surface of the touch panel and “hover operation” performed by causing a finger to be positioned at a predetermined height from the surface of the touch panel, without bringing the finger of the bare hand onto contact with the surface of the touch panel. Accordingly, a user can perform an operation with a finger covered with gloves in addition to a bare hand.
Examples of a touch panel of a type of receiving “touch operation” are disclosed in Japanese Patent Unexamined Publication No. 2009-087311 and Japanese Patent Unexamined Publication No. 2006-323457.
In an electrostatic capacitive touch panel, a two-dimensional coordinate obtained when water or the like is attached to a surface of the panel is caused to be effective in some cases. This problem can be avoided by detecting the strength of pressure on the touch panel and not detecting pressure occurring due to attachment of water or the like. For example, strain when water or the like is attached is detected by using a strain sensor and a two-dimensional coordinate when a detected strain quantity is equal to or less than a predetermined threshold value is not caused to be effective.
However, variation in strain quantity for causing an operation in an operation surface to be effective occurs in accordance with a location in which a strain sensor is disposed even though an incorrect response is prevented by providing the strain sensor. That is, since a shape of the strain sensor is smaller than the touch panel, the strain quantity becomes small at a location on the touch panel, which is far from the strain sensor and the strain quantity becomes large at a location on the touch panel, which is close to the strain sensor. For example, when the strain sensor is disposed on the center portion of the touch panel, the strain quantity is large at the center portion of the touch panel and the strain quantity is small at an end portion of the touch panel. As described above, the touch operation may or may not be caused to be effective in accordance with the location on the touch panel.
Operability and incorrect detection have the trade-off relationship. That is, as the strain quantity for causing to be effective becomes smaller, incorrect detection, for example, that an electrical noise or vibration which is not caused by an operation is determined to be effective increases. On the other hand, as the strain quantity for causing to be effective becomes larger, it is difficult to effectively detect strain at an end of the panel.
FIGS. 21A and 21B illustrate the above-described problem. FIG. 21A illustrates an operation surface 100 and a strain sensor 101. As illustrated in FIG. 21A, the strain sensor 101 is disposed at a position which is a little lower than the center of the operation surface 100 and an touch operation is performed on an A-A line of the operation surface 100, which passes through the center portion of the strain sensor 101, with the same extent of strength. FIG. 21B illustrates strain quantities detected by the strain sensor 101 at this time.
A touch position Pa on the operation surface 100 corresponds to a position on the A-A line at an upper end (an end on an upper side towards the drawing is referred to as an upper end) of the operation surface 100. A touch position Pb corresponds to a position on a position of the strain sensor 101 on the A-A line in the operation surface 100. A touch position Pc corresponds to a position on the A-A line at a lower end (an end on a lower side toward the drawing is referred to a lower end) of the operation surface 100. Since the touch position Pa is farthest from the strain sensor 101, the detected strain quantity is small, as illustrated in FIG. 21B. Since the touch position Pb is a position at which the strain sensor 101 is disposed, the detected strain quantity is large as illustrated in FIG. 21B. Since the touch position Pc is a position with a distance which is substantially half of the distance from the strain sensor 101 to the touch position Pa, the detected strain quantity is larger than the strain quantity at the touch position Pa and smaller than the strain quantity at the touch position Pb.
An operation effectiveness threshold value is set so as to determine whether or not a touch operation is performed. Since the influence of a touch operation on the strain sensor 101 is large at the touch position Pb with the surroundings 110 of the touch position Pb, a detectable strain quantity exceeds a threshold value although an operation with weak force is performed. That is, effectiveness is caused although an operation with weak force compared to surroundings is performed. The influence of the touch operation on the strain sensor 101 at the touch position Pc is not larger than that at the touch position Pb, but a detectable strain quantity in an operation with a little force exceeds the threshold value. Since the influence of the touch operation on the strain sensor 101 is very small at the touch position Pa with the surroundings 111 of the touch position Pa, a detectable strain quantity does not exceed a threshold value and it is difficult to determine the touch operation to be performed. In this manner, variation in strain quantity for causing the touch operation to be effective occurs on the operation surface 100 in accordance with the location at which the strain sensor 101 is disposed. The touch operation may also have an influence on the strain sensor 101 at the touch position Pa by decreasing the threshold value. However, decreasing the threshold value causes an incorrect response due to a noise.
Considering the circumstances, an object of the present invention is to provide an electronic apparatus in which a two-dimensional coordinate obtained through an operation of touching any point on an operation surface is caused to be effective and a two-dimensional coordinate obtained by water is not caused to be effective when the water or the like is attached to the operation surface.